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Observations of planetary material polluting the atmospheres of white dwarfsare an important probe of the bulk composition of exoplanetary material.Medium- and high-resolution optical and ultraviolet spectroscopy of seven whitedwarfs with known circumstellar dust and gas emission are presented. Detectionsor meaningful upper limits for photospheric absorption lines are measured for:C, O, Na, S, P, Mg, Al, Si, Ca, Ti, Cr, Fe, and Ni. For 16 white dwarfs withknown observable gaseous emission discs (and measured photospheric abundances),there is no evidence that their accretion rates differ, on average, from thosewithout detectable gaseous emission. This suggests that, typically, accretionis not enhanced by gas drag. At the effective temperature range of the whitedwarfs in this sample (16,000-25,000K) the abundance ratios of elements aremore consistent than absolute abundances when comparing abundances derived fromspectroscopic white dwarf parameters versus photometric white dwarf parameters.Crucially, this highlights that the uncertainties on white dwarf parameters donot prevent white dwarfs from being utilised to study planetary composition.The abundances of oxygen and silicon for the three hydrogen-dominated whitedwarfs in the sample with both optical and ultraviolet spectra differ by 0.62dex depending on if they are derived from the optical or ultraviolet spectra.This optical/ultraviolet discrepancy may be related to differences in theatmospheric depth of line formation; further investigations into the whitedwarf atmospheric modelling are needed to understand this discrepancy.

Seven white dwarfs with circumstellar gas discs I: white dwarf parameters and accreted planetary abundances